1. Field of the Invention
This invention relates to a process for producing fiberboard, and more particularly to a process in which fibrous material is impregnated with curable adhesives comprising reaction products of compounds which contain an amino (NH.sub.2) group and aldehydes.
2. Description of the Prior Art
Reaction products of compounds containing an amino group and aldehydes, otherwise known and hereinafter referred to as "amino resins", are conventionally prepared by partially reacting urea or melamine or a mixture thereof with formaldehyde at an elevated temperature to produce a high viscosity polymeric form comprising methylol units. Such polymeric form, with a suitable catalyst, is combined with fibrous particles and, under heat, is further polymerized to a rigid resin.
As a result of mechanical mixing problems caused by the high viscosity of th polymeric form and the tendency of the resin particles resulting therefrom to become unduly large, or attenuated, the initial reaction to the polymeric form must be carried out under controlled conditions. Moreover, once the polymeric form has been produced, the reaction can be prematurely "triggered" to form a rigid resin even in the absence of the catalyst, by the presence of a particular combination of temperature and acidity conditions. Procedures wherein dilute urea, formaldehyde and melamine are combined with heat and then cooled to room temperatures, do not appreciably prolong the pot life of the mixture. The resin cannot be easily stored or shipped, but must be mixed in situ by the user. Individualized mixing needs, in turn, require substantial duplication of equipment with resultant higher costs for the resin.